In the case of motor vehicles equipped with an accessory device, such as for example an air conditioning system, one of the main difficulties is to correct, in neutral operation and mainly at idle, the drop in engine speed due to the starting of the accessory device, and the increase in engine speed due to the stopping of the accessory device.
In addition, in the case of vehicles equipped with an air conditioning system and power steering or an automatic transmission, the conjunction of the resisting torques produced, on the one hand, by the starting of the air conditioning compressor and, on the other hand, by the lock of the wheels or the engaging of the hydraulic converter can, under certain circumstances, cause the engine to stall. This problem is even more crucial for vehicles comprising all three devices.
Moreover, the fall and increase in engine speed due respectively to the starting and stopping of the accessory device or devices is physiologically unpleasant for the occupants of the vehicle.
It is already known how to regulate the average idling speed of a controlled ignition engine by referring to an instruction speed. It is also known, particularly by French patent application Nos. 82/22 146 and 82/22 147, how to stabilize the neutral or idling rotation speed, i.e., to reduce as much as possible the instabilities and pumpings of the engine, by acting on the angle of ignition advance.
However, none of these solutions makes it possible for it alone to nearly completely compensate for the significant variations of speed due to the starting or stopping of accessory devices such as an air conditioning system or similar system.